Abstract
This article briefly reviews two recent lines of research that investigate the role of background knowledge in category learning and category formation. The results of several experiments show that when subjects are able to use their background knowledge to integrate the features of instances with respect to an underlying theme, they learn the categories being taught by the experimenter much more easily. In addition, the opportunity to apply background knowledge dramatically affects what categories the subjects spontaneously form when they do not receive feedback from an experimenter. The implications of these results for traditional accounts of similarity in category learning and formation are discussed.